1. Field of the Invention
The present invention relates to an end seal structure of a fuel rail (delivery pipe) for supplying high-pressure fuel, which is supplied from fuel booster pumps of electronic fuel injection-type automobile engines or the like, through a fuel injector (an injection nozzle) directly injecting the fuel into an engine cylinder. More specifically, the present invention relates to an end seal structure of a fuel rail for a gasoline direct injection engine configured to directly supply the fuel from the rail to the injector with an injection pressure in the order of 20 MPa to 70 MPa.
2. Description of the Related Art
Some exemplary fuel rails can be mentioned as the conventional fuel rails for gasoline direct injection engines of this type. For example, an exemplary fuel rail includes a main pipe and several branch pipes and is constructed and arranged such that through-holes for receiving each branch pipe are formed in an outer wall of the main pipe, each through-hole having an annular wall that projects toward the outside and inside of the main pipe, respectively, and each branch pipe being fixed to the annular wall. Another exemplary fuel rail is constructed and arranged such that a branch pipe is connected to a body, which is an accumulating vessel, directly or via a branch joint fitting (nipple). Still another exemplary fuel rail is constructed and arranged such that a socket for connection of an injector is directly attached to a rail body constituted by a tubular member such as a pipe. Further, other exemplary fuel rails may be mentioned as the fuel rail constructed and arranged such that the socket for connection of the injector is directly attached to the rail body constituted by the tubular body such as the pipe. For example, an exemplary fuel rail includes an injector holder and a fastening bracket that are directly attached to a rail body constituted by a tubular body such as a pipe to which high-pressure fuel is supplied from a high-pressure fuel pump (see Japanese Patent Laid-Open No. 2010-7651). Also, a high-pressure fuel delivery pipe for a direct injection engine includes a cylindrical body pipe into which pressurized fuel from a high-pressure fuel pump is supplied, a plurality of sockets to which fuel injection valves coupled to the body pipe and operable to be opened and closed by a control unit are coupled, and a plurality of mounting stays integrally fastened to the body pipe so as to attach the body pipe to the engine (see Japanese Patent Laid-Open No. 2011-144768).
However, the above-mentioned conventional fuel rails for gasoline direct injection engines have the following problems.
Specifically, in the above-mentioned various conventional fuel rails for gasoline direct injection engines, a rail body constituted by a tubular body such as a pipe is constructed and arranged such that an end or both ends thereof are closed, and its end rail structure is, for example as illustrated in FIGS. 6 and 7 by enlarged views, generally configured such that end caps 112A and 112B are each joined by brazing to corresponding one of the ends of the openings of a cylindrical body pipe 111. Meanwhile, a problem that is identified and should be addressed is the strength of the end caps 112A and 112B closing the both ends of the body pipe 111 in the trends of higher pressures in gasoline direct injection systems. More specifically, the following and other problems are identified. In the case of the end seal structure configured by joining the end caps 112A and 112B by brazing to the body pipe 111 as illustrated in FIGS. 6 and 7, the end seal structure is configured such that, when an internal pressure is applied in the body pipe 111 which is the rail body, a force created in a radial direction of the rail body at the time of the body pipe 111 being deformed in the radial direction (swollen outward of the pipe) is received by the brazed portions 113A and 113B, respectively, so that these brazed portions 113A and 113B become the weakest portions in terms of their strength, which makes it difficult for gasoline direct injection systems to meet their higher-pressure requirements. Further, since the brazed portions 113A and 113B are in direct contact with the fuel (pressure medium), if there is any unevenness in the shape of these brazed portions, then it tends to become a factor of breakage of the brazed portions due to concentration of stress. Also, the body pipe 111 needs to be made thicker if threading is performed on the body pipe 111 to directly fix the end caps 112A and 112B to the body pipe 111.
It is accordingly an aim of the present invention, which has been made in view of the problems found in the conventional fuel rails, to provide an end seal structure of a fuel rail for a gasoline direct injection engine, in particular in a rail body constituted by a tubular body such as a pipe constructed and arranged such that one end or both ends thereof are closed by an end cap or caps, having a simple structure and allowing the end cap portion to meet higher pressure requirements without the need of providing a thicker rail body.